Apparatus for measuring temperatures in boreholes



April 20, 1943. HENRI-GEORGES DOLL APPARATUS FOR MEASURING TEMPERATURES IN BORE HOLES Original Filed Dec. 27, 1937 few SOURCE OF EL ECTR/CHL /9 SOURCE OF E L EC TR/C/IL ENERGY SOURCE OF ELECTRICAL ENERGY INVENTOR: Henri-Georges .00,

ATTORNE 5 Patented Apr. 20, 1943 APPARATUS FOR. MEASURING TEMPERA- TURES BOREHOLES Henri-Georges Doll, Houston, Tex., assignor to Schlumberger Well Surveying Corporation, Houston, Tex., a corporation of Delaware Original application December 27, 1937, Serial No. 181,879. Divided and this application May 8, 1941, Serial No. 392,025.

8 Claims.

The present invention relates to apparatus for obtaining indications of temperatures in relatively inaccessible places, such as in bore holes drilled into the earth, for example, although it is not limited to such use.

In the current practice, it is customary to employ resistance thermometers for obtaining indications of temperatures in bore holes drilled into the earth. Usually a resistance thermometric element is lowered to different depths in the bore hole on an insulated two-conductor cable and measurements are made of variations in the resistance of the circuit by means of a Wheatstone bridge or other analogous apparatus.

As a practical matter, the cable is wound on a winch at the surface of the earth in order that the thermometric element may be raised and lowered in the bore hole and the connections between the ends of the conductors in the cable and the Wheatstone bridge are usually made through conventional slip rings and brushes. Experience has demonstrated that this apparatus is not entirely satisfactory because of errors introduced by variations in the contact resistance of the slip rings and brushes used and by variations in the resistance of the cable conductors resulting from variations in temperature at different depths in the bore hole.

In my copending application, Serial No. 181,879,

iiied December 27, 1937, for Arrangement for measuring temperatures at a distance, particularly in a bore hole, and which resulted in Patent No. 2,249,751 dated July 22, 1941, of which the present application is a division, there is disclosed apparatus which is designed to minimize such errors. This is accomplished by lowering at least one of the apices of the Wheatstone bridge into the bore hole to the level at which the measurements are to be made, thereby substantially eliminating errors introduced by variations in the resistance of the connecting cables.

The present application is addressed to analogous apparatus in which a ground return is employed for the purpose of reducing the number of conductors required in carrying out temperature measurements in a bore hole.

The invention may be better understood from the following detailed description of several representative embodiments taken in conjunction with the accompanying drawing, in which Fig. 1 is a schematic diagram of apparatus constructed in accordance with the present invention for measuring temperatures in a bore hole;

Fig. 2 is aschematic diagram of an embodi- In France January ment of the invention in which the entire Wheatstone bridge is lowered into the bore hole; and

Fig. 3 illustrates schematically a further embodiment of the invention employing only asingle conductor cable.

In the embodiment of the invention which is illustrated in Fig. l of the drawing, a temperature-responsive resistance element I ll made of a metal having relatively high temperature coeflicient of resistivity is lowered into a bore hole ll,

which usually contains a liquid L. The element 10 is connected in series with a conductor I! in the cable (not shown) on which the apparatus is suspended in the bore hole II, the upper end of which is connected to one of the apices l3 of a conventional type Wheatstone bridge l4 located at the surface of the earth.

The thermometric element I0 is connected at its lower end to a ground point IS in the liquid L in the bore hole III, which constitutes one of the apices of the bridge l4 and which is connected through a second conductor iii in the supporting cable and through a variable resistance I! at the surface of the earth to another apex l8 of the bridge l4. The bridge ll also includes two fixed resistors "Ba and I9, preferably made of constantan or manganin or any other suitable alloy having a negligible temperature coeflicient of resistivity, and a fourth apex 20. The variable. resistance I! should also preferably be made of the same material as the resistors I81; and i9.

At the surface of the earth is located a suitable source of electrical energy 2|, one terminal of which is connected to the apex 20 of the bridge l4 and the other terminal of which is connected to the ground point 22 at the surface, the circuit being completed through the liquid L and the intervening earth formations between the ground point 22 and the grounded apex IS in the bore hole 10. It may be desirablein certain cases to insert .a relatively large resistance in series with the source of electrical energy 2| in order to minimize any material variations in the current supplied therefrom. However, such a stabilizing resistance is not necessary.

A conventional type instrument 23 for measwing or recording diiferences of potential is connected to the apices i 8 and i3 of the bridge. The potential indicating instrument, 23 shouldepreferably be of the recording type so that a continuous record of potential differences, which'are related to temperatures in the bore hole, may be obtained as the thermometric element; 10 is moved through the bore hole I i.

In practice, the resistances 11, 18a and is may all have the same value, which may, if desired,

actual resistance variations in the thermometric element i0 may be measured in the conventional manner by noting the adjustment which must be made in the variable resistance I! to maintain the bridge I balanced.

Inasmuch as the cable conductors l8 and I2 are included in the two adjacent lower arms of the Wheatstone bridge ll, respectively, it will be readily'apparent that variations in the resistances of those conductors with temperature will have little or no effect on the measurements made. Furthermore, by utilizing a ground return for the energizing circuit of the bridge, only two conductors are required for making the measurements.

If desired, the entire Wheatstone bridge may be lowered into the bore hole as shown in Fig. 2. In this embodiment, the potential indicating instrument 23 is connected to the apices l8 and ii of the bridge it through the conductors 24 and 2|, respectively. A third conductor 26 is connected to the apex of the bridge I! and to one terminal of the source of electrical energy 2|, the other terminal of which is connected through a"relatively high resistance 21 to the ground point 28 at the surface. The function of the resistance 21 is to prevent any material variation in the current supplied to the Wheatstone bridge it such as might be caused by variations in the resistance of the intervening formations between the apex I! of the bridge I4 and the ground point 28 at the surface of the earth.

It is also possible to use only a single conductor for obtaining indications of temperature in the bore hole as illustrated in Fig. 3. This is accomplished by lowering the source of current into the bore hol with the Wheatstone bridge. A single conductor 29 is connected to the apex 20 of the bridge I4 and to the potential indicating instrument 23 at the surface of the earth, the other terminal of which is grounded at the point It. The potential indicating instrument 23 should preferably have a relatively'high resistance in order that the indications obtained will not be materially influenced by variations in the resistance of the intervening formations between the apex ll of the bridge and the ground point 30.

From th foregoing, it will be readily apparent that the invention provides new and improved apparatus for measuring temperatures in relatively inaccessible places such as bore holes, for example, in which errors produced by variations inthe resistance of the conductors in the supporting cable have been substantially eliminated. Moreover, by employing a ground return either for the energizing circuit or for the indicating circuit the number of conductors required for carrying out temperature measurements in a bore hole may be reduced-to a minimum.

Whil several specific embodiments have been described and illustrated here t e in e t on is notintendedtoberestrictedtheretabutissusceptibie of numerous changes inform and detailwithin the scope of the appended'claims.

I claim:

1. Apparatus for obtaining indications of temperatures in a bore hole, comprising a temperature-responsive resistance element lowered into the bore hole, an electrical network connected to said resistance element and forming a Wheatstone bridge having at least four spices, at least one of which is dispos d in the bore hole with said resistance element and i connected to ground therein, an electrical circuit connected to the apex of the bridge opposite said grounded apex and to a ground point at the surface of the earth, a second electrical circuit connected to the other two opposite aplces of the bridge. a source of electrical energy in one of said electrical circuits and electricalindicating means in the other of said electrical circuits.

2. Apparatus for obtaining indications of temperatures in a bore hole, comprising a temperature-responsive resistance element lowered into the bore hole, an electrical network connected to said resistance element and forming a Wheatstone bridge having at least four apices, at least one of which is disposed in the bore hole with said resistance element and is connected to ground therein, a source of electrical energy, an electrical circuit connecting said source to the apex of the bridge opposite said grounded apex and to a ground point at the surface of the earth, electrical indicating means and a second electrioal circuit connecting said indicating means to the other two opposite apices of the bridge.

3. Apparatus for obtaining indications of temperatures in a bore hole, comprising a temperature-responsive resistance element lowered into the bore hole, an electrical network connected to said resistance element and forming a Wheatstone bridge having at least four apioes, at least one of which is disposed in the bore hole with said resistance element and is connected to ground therein, a source of electrical energy at the surface of the earth, an electrical circuit connecting said source to the apex of the bridge opposite said grounded apex and to a ground point at the surface of the earth, electrical indicating means at the surface of the earth, and a second electrical circuit connecting said indicai ng means to the other two opposite apices of the bridge.

4. Apparatus for obtaining indications of temperatures in a bore hole, comprising a temperature-responsive resistance element lowered into the bore hole, an electrical network connected to said resistance element and forming a Wheatstone bridge having at least four apices, at least one of which is disposed in the bore hole with said resistance element and is connected to ground therein, electrical indicating means at the surface of the earth,.an electrical circuit connecting said indicating means to the apex of the bridge opposite said grounded apex and to a ground point at the surface of the earth, a source of electrical energy disposed in the bore hole with said thermometric element, and a second electrical circuit connecting said source to the other two opposite apices of the bridge.

bore hole connected to the other end of said element and to ground and extending to the surface of the earth, a plurality of electrical resistances at the surface of the earth, electrically connected to each other and to said conductors to form a Wheatstone bridge having at least four apices of which the ground connection in the bore hole constitutes one, a source of electrical energy at the surface of the earth, an electrical circuit connecting said source to ground at the surface and to the apex of the bridge which is opposite the apex in the bore hole, and electrical indicating means connected to the two other opposite apices of the bridge.

6. Apparatus for obtaining indications of temperatures in a bore hole, comprising a temperature-responsive resistance element lowered into the bore hole, a plurality of electrical resistances disposed in the bore hole with said element and electrically connected thereto to form a Wheatstone bridge having at least four apices, one of which is connected to ground in the bore hole, electrical means comprising a source of electrical energy at the surface of the earth, an electrical circuit connecting said electrical means to the apex opposite said grounded apex and to a ground point at the surface of the earth, and a second electrical circuit including electrical indicating means connected to the two other opposite apices of the bridge. 7. Apparatus for obtaining indications of temperatures in a bore hole, comprising a Wheatstone bridge lowered into the bore hole and having a temperature-responsive resistance element in one arm thereof, said bridge having at least four apices, one of which is connected to ground in the bore hole, a source of electrical energy at the surface of the eaarth, having one terminal connected to ground at the surface, an electrical conductor connecting the other terminal of said source with the apex of the bridge opposite said grounded apex, electrical indicating means at the surface of the earth, and electrical connections between the two other opposite apices of the bridge and said indicating means.

8. Apparatus for obtaining indications of temperatures in a bore hole, comprising a Wheatstone bridge lowered into the bore hole and having a temperature-responsive resistance element in one arm thereof, said bridge having at least four apices, one of which is connected to ground in the bore hole, electrical indicating means at the surface of the earth, having one terminal connected to ground at the surface, an electrical conductor connecting the other terminal of said indicating means to the apex of the bridge opposite said grounded apex, and a source of electrical energy disposed in the bore hole with said bridge and connected to the two other opposite apices thereof.

HENRI-GEORGES DOLL. 

